1. Field of the Invention
This invention relates generally to wireless communication devices, and more specifically, to a radio frequency power amplifying system.
2. Related Art
In personal communications devices such as cellular telephones, there is a trend toward minimizing size and weight. The size and weight are, however, contingent upon the size and weight of the various components that make up the personal communications device. Briefly, the smaller the various components of the personal communications devices, the smaller the size and overall weight of the personal communications device. Many personal communications devices have an overall size and weight that is, to a large degree, dominated by the size and weight of the battery that provides a supply voltage to the personal communications device. This is so because consumers want personal communications devices to have a prolonged operating time during usage.
As operating time requirements and power consumption of the personal communications device during operations increase, the size of the battery required to perform under these circumstances will also increase. Thus, the reduction of current and power consumption in the personal communications devices and the reduction in the size of components leads to a reduced battery size. Alternatively, where the size of the battery remains constant, the operating time of the personal communications devices can be increased.
In typical personal communications devices such as, for example, a portable transceiver, efficiency of the device is optimized at a maximum power output without regard to whether or not the maximum power output is actually needed. Thus, as the power output of a typical transceiver drops below the maximum power output level, the efficiency of the transceiver also drops. This reduces the battery voltage and thus limits the operation time of the transceiver.
Therefore, there exists a need in the industry for a power amplifying system that makes efficient use of broad operating power ranges.
The invention provides a radio frequency (RF) power amplifying system for a personal communications device. In one embodiment, the power amplifying system includes a power controller and one or more power amplifiers comprising power transistors and bias circuitry. The bias circuitry is decoupled from the collector terminals of the power transistors to enable substantially reduced supply voltages and consequently a reduced power consumption for the power amplifiers. The bias circuitry provides current to the base of the one or more power transistors in such as manner as to maintain the power transistors in substantially linear operation throughout the variation in collector supply voltage as supplied by the power controller.
In one embodiment, the bias circuit is supplied with a reference voltage that is independent of the regulated supply voltage provided by the power controller. The power controller monitors the current draw of the bias circuit of each power amplifier. The supply voltage is automatically adjusted based on the current draw of the bias circuit, which is proportional to the power output level of each power amplifier. The bias circuit provides substantially constant current to the base terminals of the power transistors for each predefined power output level of each power amplifier, thus maintaining substantially linear operation of the power transistor.
In another embodiment, the supply voltage from the power controller and a separate reference voltage are both fed to the bias circuit. The supply voltage from the power controller acts as a xe2x80x9ccontrol signalxe2x80x9d to the bias circuit, causing the bias circuit current to vary automatically as a function of the supply voltage, thus automatically adjusting the bias point of the power transistors to maintain substantially linear operation.